Part 139. The sunflower family (Compositae). Examples: Jerusalem artichoke (Figs. 59 I-IV), lettuce (Figs. 75-77), and wormwood (Fig. 155).

Formulas of Helianthus, Lactuca, Artemesia, and Compositae are given on pages 420, 421.

More than a tenth of all the species of flowering plants belong to this the largest family of seedworts. The very characteristic inflorescence is sometimes mistaken for a single flower, and was indeed called a "compound flower" by the early botanists. In reality, as will be readity seen, the small flowers are borne on a more or less flattened expansion of the peduncle, called the receptacle, and form a compact head surrounded by an involucre of bracts resembling sepals. As if to increase the deception the outer row of florets often have what are called strap-shaped corollas formed by a coalescence of the petals into one flat piece (Fig. 59 II, III), somewhat as in the Indian tobacco but more complete; and these corollas radiate so as to look like petals. The inner part of the head in such cases as the sunflower is made up of regular florets (Fig. 59 III). Many members of the family have only regular florets, while still others have all the florets strap-shaped or sometimes labiate.

The calyx may consist of a few papery scales, or of numerous bristles forming what is termed the pappus.1 Sometimes through a prolongation of the torus above the fruit a sort of parachute is formed as in lettuce (Lactuca, Fig. 76). The one-seeded fruit of Compositae is commonly called an achene, although morphologically it is very different from such a simple achene as that of the crowfoots.

1 Pap'-pus > Gr. pappos, grandfather, applied to the thistledown in allusion to white hair.

In spite of wide diversities in structural detail the members of this vast family may generally be recognized as herbs with milky or watery juice; flowers in dense heads having a calyx-like involucre, gamopetalous, regular or irregular; stamens five, syngenesious, but with distinct filaments inserted on the corolla, and the pollen-sacs straight; ovary inferior, with a single ovule; fruit achenial, often with pappus.